K Frame Forcing Cone Failure


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308win
April 10, 2010, 10:45 AM
How many rounds would you expect before forcing cone fails when firing high pressure .357 Magnum 125gr loads? If I fire regular pressure loaded with heavier bullets should I expect issues. I have a late 70's production target Model 19 Combat Magnum with a 6" barrel that probably has less than 400 rounds through it but most of them have been 125gr maximum loads.

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gwnorth
April 10, 2010, 11:32 AM
I would think you would be good for thousands of rounds at least (a few k's anyway). It's also not something that is guaranteed at all. Shooting light weight, hot .357 loads does clearly increase the likelihood of forcing cone cracks, but it in no way assures that it will happen. I know a couple of folks with model 19's and other k-frames with many, thousands of rounds through them and they are still tight, sound and shoot just fine.

To minimize the risk of a catastrophic failure, I would stick with 158gr loads, and do in my model 65-3.

harmonic
April 10, 2010, 12:38 PM
FIY:

The 125 grain bullets driven to maximum velocities used large charges of relatively slow-burning powders. Handloaders know the powder types as WW296 and H-110, among others. The combination of slow ball-type powders and the short bearing surface of the 125 bullets allows prolonged gas cutting of the forcing cone and top strap area, accelerating erosion and wear.

Borescope studies of rifle, machine gun, and auto cannon chamber throats shows a lizzard-skin-like texture due to this gas cutting damage, called "brinelling". The results of brinelling are fine microcracks that weaken the surface of the steel, and further promote erosion. In machine guns and auto cannons, barrel life is measured in terms of "useable accuracy", and round counts that determine this are based on group sizes at engagement ranges.

In the K-frame magnums, the forcing cone dimensions combined with the barrel shank dimensions results in a relatively thin shank at the 6 o'clock position, where a machine cut is made to clear the crane. This is usually where the forcing cone cracks. The L and N frames use much beefier barrel shanks and do not have this cut. S&W intended the K frame magnums to be "carried much and fired seldom" service arms, designed to fire .38 Specials indefinitely, with light to moderate use of .357 Magnums. You notice that S&W has discontinued production of K frame .357 magnums, no doubt due to product liability issues and a couple generations of K frame magnum experience.

Radagast
April 10, 2010, 01:40 PM
http://www.gunblast.com/Butch_MagnumLoads.htm Is the best essay I've seen on the issue.

Onmilo
April 10, 2010, 02:51 PM
Gunblast=sound advice
N or L frame blaze away with +p and any magnum load.

K frames work best with 140 grain magnums and heavier and avoid the +P .38Special stuff altogether.

308win
April 10, 2010, 02:53 PM
I don't remember what I loaded with but it wasn't 296 or 110. I only have 50 or so of the 125gr left and I will only use those for SD load.

Steve C
April 10, 2010, 03:45 PM
Read this: http://www.gunblast.com/Butch_MagnumLoads.htm

snooperman
April 10, 2010, 05:52 PM
shooting hot loads over many years. My model 19 went out of timing several times. I have hunted deer and wild boar with it on my land , and have found the K frame lacking. Hence, I only hunt with my Rugers now. If you plan to shoot a lot of 357 magnum loads , buy a Ruger . I do my own reloading and My Ruger blackhawk and sixes have never let me down with my hot loads.

roaddog28
April 10, 2010, 07:40 PM
shooting hot loads over many years. My model 19 went out of timing several times. I have hunted deer and wild boar with it on my land , and have found the K frame lacking. Hence, I only hunt with my Rugers now. If you plan to shoot a lot of 357 magnum loads , buy a Ruger . I do my own reloading and My Ruger blackhawk and sixes have never let me down with my hot loads.

Hi,
I believe the statement above is accurate for the K frame magnum. There are many articles about the forcing cracking, shooting loose and going out of time.
I have a model 66 4 inch and still believe it is the best handling revolver Smith ever made. But I shoot 38 specials almost all the time with a occasional few rounds of 158gr 357s. The K frame magnum was meant to shoot 357s only on occasion.
I leave my heavy duty shooting of full power 357s to my Ruger GP100 4 inch or my Ruger Police Service Six 4 inch. Both can take it. Smith has the 586/686 and 27/28 which would be good choices too.
Here is another link on a good article on the K frame magnums shooting 357s.
http://www.hipowersandhandguns.com/model_19_family.htm

Good luck,
roaddog28

dispatch
April 10, 2010, 08:06 PM
I just understand why anyone would use less than a flat nosed or SWC 158 grain slug.

Confederate
April 10, 2010, 11:20 PM
This comes up repeatedly on this forum, and there's no easy answers. The best approach is to not wear out a great gun by shooting magnum loads. If you want to shoot extensive magnum loads, get a Ruger Security-Six. And speaking of the Security-Sixes, quite a few had notches cut into the bottom portions of their forcing cones, and they weren't problems.

The K-frame S&Ws had structural problems other than forcing cone weakness. The blast was distributed throughout the frame, which was weakened by the side plate. Light-bullets tended to eat away at the forcing cones while the heavier bullets adversely affected the frame. Frame warping caused the timing to fail while erosion leeched the carbon from the forcing cone, causing it to crack. Stainless steel resisted erosion more than standard steel, but it wasn't immune.

A gun with 6,000 hot magnum loads through it would likely be well shot out, and probably would have required retiming twice. A Security-Six would just be getting started -- and there are cases where people have fired well over 30,000 rounds of hot magnum rounds with no problem whatsoever.

If you have a 19/66 and are determined to shoot light bullets in factory magnum loadings, you might want to consider hard chroming your pistol. It won't stop warping, but it may slow down leeching and gas cutting.

If I had a nice Model 66, I'd shoot mostly .38s in it (which I do with my Rugers as well).

VA27
April 10, 2010, 11:34 PM
It's not just K-frames. I've shot loose 2 Model 29 N-frames and a 681 L-frame. The 681 was rebuilt by the dept armorer 4 times. He said the next time it would have to go back to Smith, 'cause he'd done all he could do.

If you use any piece of machinery a lot you will wear it out, it's just the nature of mechanical things. Do you still have your first automobile, lawn mower, chain saw?

Shoot it and don't worry about it, that's what they're made for. When it needs a tune-up, send it to a specialist and get it fixed.

madcratebuilder
April 11, 2010, 08:53 AM
The .357 K frame was intended for duty use. Practice with .38 and carry .357. I was never intended for a steady diet of .357. If you want to shoot .357 all the time get a L or N frame.

evan price
April 11, 2010, 11:26 PM
I load "Cowboy" .357 loads for my "K"-frames using lead 158-SWCs or 125-TCs. Keep the velocity down, use a fast powder, and you'll have no problem. The real cone-eaters were the 110-grain Magnums travelling 1500 FPS or more. Stay under 1100 FPS and you'll do OK.

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